Logical operators in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of combined logical operators

What is the output of this Swift code snippet?

Swift

let a = true
let b = false
let c = true
print(a && b || c)

A true

B false

C nil

D Compilation error

💡 Hint

Remember that && has higher precedence than || in Swift.

The expression a && b || c is evaluated as (a && b) || c. Since a && b is false, the result depends on c, which is true. So the final result is true.

❓ Predict Output

intermediate

Result of negation and OR operator

What does this Swift code print?

Swift

let x = false
let y = true
print(!x || y)

A nil

B true

C false

D Runtime error

💡 Hint

Negation (!) flips the boolean value.

!x is true because x is false. Then true || y is true. So the print outputs true.

❓ Predict Output

advanced

Output of complex logical expression

What is the output of this Swift code?

Swift

let p = false
let q = true
let r = false
print((p || q) && !r)

A Compilation error

B nil

C true

D false

💡 Hint

Evaluate inside parentheses first, then apply negation and AND.

p || q is true because q is true. !r is true because r is false. So true && true is true.

❓ Predict Output

advanced

Value of variable after logical operations

What is the value of variable result after running this Swift code?

Swift

let a = true
let b = false
let c = true
let result = !(a && b) && (b || c)
print(result)

A true

B nil

C Compilation error

D false

💡 Hint

Break down the expression step by step.

a && b is false. Negation !(false) is true. b || c is true. So true && true is true.

❓ Predict Output

expert

Output of chained logical operators with precedence

What does this Swift code print?

Swift

let x = false
let y = true
let z = false
print(x || y && !z || false)

A nil

B false

C Compilation error

D true

💡 Hint

Remember that && has higher precedence than ||, and negation applies before &&.

Evaluate !z first: true. Then y && true is true. So expression is x || true || false, which is true.

Practice

1. Which logical operator in Swift returns true only if both conditions are true?

easy

A. == (Equality)

B. || (OR)

C. && (AND)

D. ! (NOT)

Solution

1. Step 1: Understand the AND operator

   The AND operator (&&) returns true only when both conditions it connects are true.

2. Step 2: Compare with other operators

   The OR operator (||) returns true if at least one condition is true, NOT (!) flips true to false and vice versa, and == checks equality, not logical combination.

3. Final Answer:

   && (AND) -> Option C

4. Quick Check:

   AND = && [OK]

Hint: AND needs both true; look for && operator [OK]

Common Mistakes:

• Confusing AND (&&) with OR (||)
• Thinking NOT (!) combines conditions
• Mixing equality (==) with logical operators

2. Which of the following is the correct syntax to negate a Boolean value isActive in Swift?

easy

A. !isActive

B. not isActive

C. isActive!

D. isActive.not()

Solution

1. Step 1: Recall the NOT operator syntax

   In Swift, the NOT operator is written as an exclamation mark (!) placed before the Boolean variable to flip its value.

2. Step 2: Check each option

   !isActive is the correct syntax. The other options are not valid Swift syntax for negation.

3. Final Answer:

   !isActive -> Option A

4. Quick Check:

   NOT = ! before variable [OK]

Hint: Use ! before variable to negate Boolean [OK]

Common Mistakes:

• Writing 'not' instead of '!'
• Putting ! after variable name
• Using method calls like .not()

3. What will be the output of this Swift code?

let a = true
let b = false
print(a || b && !b)

medium

A. Syntax Error

B. true

C. false

D. nil

Solution

1. Step 1: Evaluate the NOT operator

   !b means !false which is true.

2. Step 2: Evaluate AND operator

   b && !b is false && true which is false.

3. Step 3: Evaluate OR operator

   a || (result of AND) is true || false which is true.

4. Final Answer:

   true -> Option B

5. Quick Check:

   OR with true = true [OK]

Hint: Remember NOT first, then AND, then OR [OK]

Common Mistakes:

• Ignoring operator precedence
• Evaluating OR before AND
• Misunderstanding ! operator

4. Identify the error in this Swift code snippet:

let x = true
let y = false
if x || && y {
    print("Yes")
}

medium

A. Missing parentheses around conditions

B. print statement syntax error

C. Variables x and y are not Boolean

D. Incorrect use of logical operators together

Solution

1. Step 1: Analyze the if condition syntax

   The condition uses 'x || && y' which combines OR (||) and AND (&&) operators without a proper operand between them.

2. Step 2: Identify the logical operator misuse

   Logical operators must connect two Boolean expressions. Here, '|| &&' is invalid syntax.

3. Final Answer:

   Incorrect use of logical operators together -> Option D

4. Quick Check:

   Operators must connect expressions properly [OK]

Hint: Operators need operands on both sides [OK]

Common Mistakes:

• Writing two operators without a condition between
• Assuming parentheses fix operator misuse
• Confusing variable types with operator errors

5. You want to check if a number n is between 10 and 20 inclusive in Swift. Which condition correctly uses logical operators?

hard

A. n >= 10 && n <= 20

B. n > 10 && n < 20

C. n >= 10 || n <= 20

D. !(n < 10 && n > 20)

Solution

1. Step 1: Understand the range condition

   To check if n is between 10 and 20 inclusive, n must be greater than or equal to 10 AND less than or equal to 20.

2. Step 2: Evaluate each option

   n >= 10 || n <= 20 uses OR which is incorrect because it allows values outside the range. n > 10 && n < 20 excludes 10 and 20 by using > and <. !(n < 10 && n > 20) negates an impossible condition and is incorrect.

3. Final Answer:

   n >= 10 && n <= 20 -> Option A

4. Quick Check:

   Use AND for range checks [OK]

Hint: Use && to combine lower and upper bounds [OK]

Common Mistakes:

• Using OR instead of AND for range
• Excluding boundary values by using > or <
• Using negation incorrectly for range